Method for the production of an oxide ceramic shaped part and a part produced by such method

ABSTRACT

A method for producing an oxide ceramic shaped part includes pressing a powder provided with a binding material or a powder mixture of an oxide ceramic into a shaped part, pre-sintering the shaped part at substantially atmospheric pressure and a temperature of 600 to 1,300° C., and evacuating a closed container in which the pre-sintered shaped part is disposed with the shaped part having a maximum density of 10 to 90%. The container is at an absolute pressure of less than 40 mbar. Subsequently, an infiltration material is applied onto the shaped part via infiltration with the infiltration material operating to seal off the shaped part relative to the surrounding atmosphere. The length of time of the infiltration is preferably 1 to 10 minutes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims foreign priority benefits under 35 U.S.C. §119from German patent application Ser. No. 10 2004 004 059.1 filed Jan. 27,2004.

TECHNICAL FIELD

The present invention relates to a method for producing an oxide ceramicshaped part, as well as to an oxide ceramic shaped part.

BACKGROUND OF THE INVENTION

Methods for the production of an oxide ceramic shaped part have beenknown for a long time. For example, it is known from WO 95/35070 toproduce a ceramic shaped part. In this approach, the ceramic isinfiltrated. The production of an oxide ceramic shaped part of this typeis, however, relatively time-consuming; the step alone of theinfiltration that is undertaken in connection with this approach,requires, for example, 4 hours.

Furthermore, it is known from EP-A 1 834 366 to produce a ceramic piecethat is produced via the infiltration of a melted matrix material intothe hollow space of a blank. A particular particle size with twodifferent size gradations is provided for the infiltration substance. Inconnection with this approach, a covering material is used that isprovided with a soluble salt that must be removed after the infiltrationand the solidification step. The disadvantage of this approach is theneed for the high process temperature during the shaping and thecomplicated hardware-intensive production.

The publication WO 88/02742 discloses the production of a ceramiccomponent having a hardened outer surface. A porous AlO₂ blank isinfiltrated with a zirconium oxide infiltration material so that thefinished ceramic work piece comprises a volume portion of 1 to 15%zirconium oxide and, thus, the so-formed aluminum oxide ceramic issolidified. This process requires several infiltration steps and issuitable if a relatively soft ceramic such as aluminum oxide is to behardened, while it is to be understood that a zirconium oxide ceramicwith a high critical stress intensifying factor cannot be furtherhardened or strengthened via the addition of zirconium oxide. A ceramicof this type exhibits a strengthening only on its outer surface and, toproduce a suitable work piece via this approach, the process steps mustfrequently be implemented in a serial manner.

Furthermore, DE-A1 198 52 740 discloses the configuration of a cap, orthe configuration of other dental pieces, of aluminum oxide ceramic. Thepre-sintered shaped part is infiltrated in the heated condition with aglass, which melts upon the introduction of the shaped part into thesintering oven. The infiltration requires, in connection with thisapproach, a timeframe of approximately 4 hours and a high presstemperature. On top of this, the process is decidedly difficult tocontrol and the mechanical properties of the dental piece arecorrespondingly poor.

Additionally, DE-A1 100 61 630 discloses the production of a fullceramic dental restoration piece comprised of a dental ceramic ofzirconium oxide and aluminum oxide, whereby an infiltration with glassin a volume range of 0 to 40% is undertaken. This approach additionallyrequires, in connection with the deployment of such a dental restorationpiece, the use of a mixture ceramic. A disadvantage of this approach isthe reduced securement properties of the ceramic, which has beensolidified via the glass phase.

Moreover, EP-A1 1 025 829 discloses the production of a cap of a ceramicmaterial infiltrated with glass. In order to provide the desiredtranslucence, two additional coatings are provided, which are appliedonto the cap. In connection with the preparation of the dentalrestoration pieces, it is, due to aesthetic reasons, critical that thenatural dental enamel be simulated, such natural dental enamel having anincreased translucence while the dentine has a reduced translucence. Inthis connection, the coatings 7 and 6 are provided in accordance withthe disclosed approach. In a process of this type, the detailed furtherworking involving the grinding of the infiltrated fixed body into apowder is disadvantageous, but, additionally, the reduced securementproperty of the ceramic solidified via the glass phase is alsodisadvantageous.

DE-A1 101 07 451 discloses a process for the production of an oxideceramic shaped part that is formed from a zirconium or aluminum oxideceramic via milling with a large CAD/CAM technology system afterpre-sintering. Thereafter, the milled blank is sintered under nopressure at 1200 to 1650° C. The thus produced oxide ceramic phaseexhibits a reduced translucence as compared to a high-temperatureisostatically pressed ceramic, the mechanical properties are worse thanthose of a high-temperature pressed ceramic, and such ceramics aredifficult to etch.

CH-A5 675 120 discloses zirconium oxide mixture ceramics, which comprise7 to 12% by weight PiO₂ and other grain growth limiting andstabilization suitable additives. These can also comprise 0 to 30% byweight Al₂O₃. The powder mixture is sintered at a temperature from 1100to 1300° C. The disadvantage of this ceramic is that the achievablethickness lies at only 98% of the theoretical thickness (TD) and,consequently, is less than that of a high-temperature pressed ceramic.The production of a retentive design on the outer surface is, with thisceramic, possible only with difficulty.

Additionally, the publication “Heiβisostatisches Pressen” from D. W.Hofer (Heiβisostatisches Pressen, in: Technische Keramische Werkstoffe,Fachverlag Deutscher Wirtschaftsdienst, Hrsg. Kriegesmann J., Kap.3.6.3.0, pp. 1-15. January 1993) discloses that work pieces can beproduced via high-temperature pressed processes in which the structuresthereof scarcely exhibit any defect locations and the thicknesses ofwhich are nearly those of the theoretically possible values. In order toachieve these properties, however, a pressure of between 30 to 200 MPais required for the sintering temperatures. Moreover, an inert gasatmosphere follows the step of the pressure treatment. Correspondingly,this technique and the attendant hardware-intensive work requireconsiderable effort and outlay. This process is thus disadvantageous inthat it is costly and involves complicated processing technologies andtheir attendant high capital and energy costs so that, for example inconnection with small enterprises, such as dental laboratories, it isnot possible for such enterprises themselves to perform this process.

OBJECTS AND SUMMARY OF THE INVENTION

In contrast, the present invention offers a solution to the challenge ofproviding a method for the production of an oxide ceramic shaped part aswell as an oxide ceramic shaped part itself, that is more suitable forthe realization of a dental restoration piece and that permits acost-optimized production with a simultaneously improved aestheticappearance without degrading the use properties of the thus-producedshaped part and offering, especially, the possibility to produce aretentive design and to ensure the securement of the shaped part on thenatural tooth.

Surprisingly, the inventive configuration of an infiltration coating orcovering on the relevant regions of the oxide ceramic part permits therealization of an increased securement of the entire oxide ceramic part.Evidently, the covering, or the at least partial covering of the oxideceramic part with the coating imparted by the infiltration, stabilizesthe oxide ceramic shaped part to such an extent that a clearly improvedfracture strength approaching 6.5 MPa m^(1/2) can be achieved.

In a surprising manner, the inventive solution also leads to animprovement of the aesthetic appearance of a dental restoration piece ifthe inventive oxide ceramic shaped part is used as the dentalrestoration piece. The infiltration coating has a higher translucencewhile the infiltration-free inner region or core of the oxide ceramichas a reduced translucence and, in connection with the realization of azirconium oxide ceramic, the coating is practically white. Thissimulates the human tooth in a surprisingly simple manner and isachieved without any need to deploy mixture ceramics, if such isdesired.

Due to the possible or optional omission of an additional mixed ceramic,the therewith connected problems also drop out such as the longerprocess time, the securement problems, and the required coatingthickness of the mixture ceramic. In contrast, the inventive solution issuitable for the realization of small-scale or closely-spaced members,yet nonetheless aesthetically very attractive, dental restorationpieces. In particular, if the infiltration coating comprises a silicatephase, this can, for example, be etched away with HF and an adhesivebinding with other work pieces can be realized.

The inventive solution permits, in a surprisingly simple manner, theachievement of the same securement properties that can be achieved withhot isostatic presses, whereby the time consuming hot-press process canbe avoided. The biaxial securement property is, in connection with oneembodiment of an oxide ceramic connection part, not less than 800 MPa.The fracture mechanism properties of the pure crystalline oxide ceramicphase are approximately 6.95 MPa m^(1/2), as determined in accordancewith the Indenter process and calculations in accordance with Evans &Charles critical tension intensification factors IIC and, in fact, liecomparatively higher than even those of corresponding high-temperaturepressed ceramics. It is surprising in this connection that theproperties of the hot-pressed materials, even those with predominantlytetragonal zirconium oxide as the crystalline oxide ceramic phase, havebeen duplicated. Preferably, the thickness of the inventive infiltrationcoating is between 2 to 30%; in an advantageous configuration between 5and 20%; and, for practical purposes, between approximately 10 to 15%,each respective selected thickness being a function of the respectivelargest diameter of the oxide ceramic part.

The coating that at least partially covers the core formed of anon-metallic, inorganic phase is relatively less resistant to acids thanthe pure crystalline oxide ceramics in the core. The coating can therebybe easily etched. The chemical resistance is, however, not substantiallyless than that of the core, if the covering coating comprises onlymicro-crystal zirconium oxide.

Due to the reduced chemical resistance of the coating that at leastpartially covers the core, a retentive design can be achieved there atvia etching. The depth of this retentive design can be determined viathe etching means, its concentration and the application time during theetching process. This depth corresponds in an inventive manner to, atthe most, the thickness of the covering coating, as the core issubstantially more resistant to chemical attacks than the coveringcoating.

In the realization of the inventive process, a pre-sintering to achieve50% of the theoretical thickness in atmospheric air is undertaken at nopressure following the pressing of the oxide ceramic blank. In therealization of the inventive process, a powder or a powder mixture isprovided as the outlet material, which is formed out of thecorresponding oxide ceramic or mixture ceramic. The powder is preferablyin the form of a granulate and is mixed with a binding material.Preferably, the binding material can be comprised of ethylene waxmaterial, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl acetate,polyvinyl butyral, or cellulose.

The pre-sintering temperature amounts to clearly less than the sinteringtemperature and can lie, for example, between 600 and 1300° C. and,preferably, between 1000 and 1200° C.

To achieve the inventive solution, it is advantageous to evacuate thepartially sintered part. In this connection, in accordance with theinvention, less than 50 mbar, such as, for example, 20 mbar, ispreferred. The low pressure is applied, for example, for 1 minute up to4 hours such that a pressure equalization in the sense of the formationof a vacuum in the interior of the partially sintered oxide ceramicshaped part is formed. In connection with this evacuation, the gases areremoved from the porous, partially sintered in-process part body. Duringthis time, the inventive sol. to be deployed for preparing the furthermaterials that are to be formed, is mixed. In a conventional manner, theformation of these further materials is undertaken following theevacuation in a low pressure atmosphere.

It is particularly advantageous, in connection with the inventivemethod, that the penetration of a precursor of a non-metallic, inorganicphase has shown its worth, such precursor comprising, for example, aprecursor of a vitreous-amorphous phase and a solvent.

In accordance with the present invention, it is particularlyadvantageous if the infiltration material is available as a sol. and isfurther reacted into a gel. These are preferably precursor products of aglass or ceramic material. Via the low pressure, the mixed sol. issuctioned into the low pressure chamber and there follows a penetrationover an inventive, decidedly short time, such as, for example,preferably, 1 minute. In this manner, there is achieved an infiltrationcoating with the desired coating thickness, which permits the setting oradjustment thereof via the infiltration time, the viscosity of thesolution, but as well, the porosity of the partially-sintered ceramicpart.

Surprisingly, the formation of the infiltration coating in a simplemanner permits the realization of a decidedly uniform coating. Due tothe short infiltration time, the infiltration fluid only has time forthe outer surface of the in-process part body to be covered. Viaaeration of the low pressure chamber, the infiltration material ispractically suctioned in. It is to be understood that the viscosity ofthe preferably gel-formed infiltration material substantially influencesthe penetration depth. A reduced viscosity produces, due to the reasonof the capillary working of the pores of the in-process part body, alarge coating thickness of the infiltration coating, while a highviscosity reduces the penetration depth. Preferably, the coatingthickness amounts to approximately 0.5 mm. In a modified embodiment, thecoating thickness of the infiltration coating is approximately 1.5 mm,which corresponds to the coating thickness of the dental enamel, butthis coating thickness can be adjusted to more or less, as well.

Immediately after this step, there follows an aeration of the lowpressure chamber and the solidification of the applied solution into agel is undertaken via heating at the pre-selected sintering temperaturein an ambient atmosphere. The sintering temperature is, for example,1300 to 1550° C. and the sintering follows under an ambient pressure atan ambient atmosphere. Via the inventive process, the sinteringproperties of the pure crystalline oxide ceramic phase are improvedwhile, via a covering coating formed from a non-metallic, inorganicphase of the previously evacuated, partially-sintered shaped part, thepenetration of gases into the porous structure of the partially-sinteredpart is prevented, whereby a complete dense sintering of the ceramic isachieved.

The inventive oxide ceramic shaped part can be pre-pressed in a desiredform. It is also, however, possible to undertake a milling or anothertype of cutting or machining in order to produce a shaped part from theceramic in-process part body and, in fact, to accomplish such, eitherafter the pre-sintering or after the sintering. With respect to such anundertaking after the pre-sintering, the advantage is gained that theshaping is possible in a relatively easy manner in that the finalhardness has not yet been reached. In contrast, in connection with suchan undertaking after the sintering, a very hard work piece such as adiamond-cutting disc must be used whereby, to be sure, the shapeintegrity is not degraded by a further shrinking process.

In accordance with the present invention, an oxide ceramic shaped partwith a theoretical thickness of 99.9% is produced via, for example,sintering at 1480° C., whereby it is advantageous that, during thesintering in an ambient atmosphere, the shaped part is worked so thatthe shrinkage factor is less than that of a high-temperature isostaticpress process.

The inventive process permits the preparation of a substantiallytetragonal phase with reduced cubical phase components, provided that asintering temperature of 1500° C. is not exceeded. In accordance withthe present invention, in a surprising manner, a translucence profile isrealized that heretofore could only be realized via a hot-press process.Additionally, in contrast to a hot-press ceramic, the advantage isobtained that an adhesion via etching on the infiltration coating ispossible without further effort.

The present invention is particularly advantageous in connection withzirconium oxide ceramic or mixture ceramics having a high zirconiumoxide portion, whereby, as well, suitable doping—such as withyttrium—and mixing—in can be advantageous. In connection with such hardceramics, the bending strength in the core is high, the fracturestrength, in contrast, is particularly good in the infiltration coating,which is formed from the crystalline oxide ceramic phase and theinfiltration phase that penetrates the crystalline oxide ceramicphase—also called infiltration.

The thus-produced inventive oxide ceramic composite shaped partcomprises, consequently, in its pure crystalline oxide ceramic core, theoptical and mechanical properties which even equal the values of thoseproperties in the high-temperature isostatic pressed materials. Theproperties of the pure crystalline oxide ceramic phase are, evidently,realized by the reason of the thickness of the structure.

In one embodiment, following the finish sintering, there is effected, toinventively produce an oxide ceramic composite shaped part, a process inwhich a material reduction working occurs that is, preferably, performedby CAD/CAM technology. In this connection, the covering coating iscompletely or partially reduced away and the translucent core comes tothe outer surface. In this manner, the final shaping of the oxideceramic composite shaped part can subsequently occur. If the coveringcoating remains in a partially covering manner on the outer surface,this can be removed in a following step via etching.

A retentive design can be maintained in the regions where the outercoating still remains. At the same time, a thick, translucent structureappears on those portions of the outer surface at which the coating hasbeen removed. In this manner, there is produced, in a surprisinglysimple manner, an aesthetic appearance that corresponds to that producedin connection with comparable hot isostatic press work pieces. Due tothe high density of the structure, a high light transmission capability(translucence) is achieved that corresponds to that of hot isostaticpressed ceramic.

To configure a dental restoration piece, a single coat mixture issubsequently applied in order to produce an even more improved aestheticappearance. In the regions in which a retentive design was produced, theuse of suitable desired adhesive systems is possible. Preferably, anadhesive system is deployed. In accordance with the present invention,an adhesive securement is possible in a surprisingly simple manner whichis not possible with respect to corresponding hot isostatic pressed workpieces. In connection with the securement materials, chemical,light-hardenable, or dual hardenable material are preferred. Cementingmaterials are, for example, zinc phosphates. The inventive oxide ceramiccomposite shaped part offers, in this manner, an improved adhesiveprocurement possibility with the same aesthetic appearance as hotisostatic pressed, comparable materials. Moreover, the sintering processis substantially simpler and is, consequently, in contrast to the hotisostatic press process, considerably more cost favorable.

The inventive solution permits a plurality of oxide ceramic parts to beproduced. In this connection, dental restoration pieces are producedsuch as inlays, onlays, crowns, partial crowns, veneers, facets,bridges, caps, brackets and abutments, but also alluvial materials, andalluvial material components and frameworks.

Also, it is basically possible to exploit the advantages of theinventive process in connection with other deployed ceramic pieces suchas, for example, the preparation of synthetic joints, whereby the outersurface infiltration coating offers favorable properties in view of thereduced abrasion with, at the same time, good hardness and a glass-hardouter surface; however, surgical implants or components thereof areequally amenable to such preparation. Also, endodontic parts such asroot posts can be produced by the inventive process whereby the goodadhesion on other parts can be exploited.

The length of time of the production of an inventive ceramic blank isstrongly dependent upon the length of time required for thedesiccation—that is, the creation of the low pressure environment. Thepreparation of the infiltration material requires, in connection withone advantageous embodiment of the invention, a not inconsiderablemixing time and standing time. The determination of the time frame can,however, be favorably influenced by the mixing of the infiltrationmaterial already before the process has begun—that is, for example,while the blank is pressed or, at the latest, during the pre-sintering,so that this mixing time does not add onto the cycle time for thepreparation of a finished oxide ceramic part.

The pure infiltration time can, for example, amount to 1 or 2 minutesand can last, in any event, typically less than 10 minutes while thefinish infiltration occurs in accordance with the respective selectedtemperature curve of, for example, 30 to 60 minutes.

Further advantages, details, and features are described in thehereinafter following descriptions of several embodiments of the presentinvention with reference to the drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic perspective view of an arrangement for performingthe inventive infiltration method for preparing an infiltration coatingon an oxide ceramic part;

FIG. 2 is a graphical view of the infiltration coating thickness versusthe infiltration time;

FIG. 3 is a schematic perspective view of a sintering oven for use inconnection with the inventive infiltration method for preparing aninfiltration coating on an oxide ceramic part;

FIG. 4 is a flow chart of the steps of one implementation of the methodof the present invention; and

FIG. 5 is a flow chart of the steps of another implementation of themethod of the present invention.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates an arrangement for performing theinventive infiltration method for preparing an infiltration coating onan oxide ceramic part. The blank 10, which subsequently forms the oxideceramic part, is pre-sintered and is disposed in a beaker 12. The beaker12 is disposed in a desiccator 14 on whose cover a drip funnel 16 ismounted.

Moreover, the desiccator comprises, in a conventional manner, alow-pressure connection hose 18 that is connected with a low-pressurepump. In a conventional manner, the polished sealing edge 20 of thedesiccator closes upon the creation of a low pressure environment in thedesiccator and can be opened after the venting of the desiccator. Thedrip funnel does not have a pressure compensation but is, however,provided with a stopcock 22 that permits a fine adjustment of the driprate.

The infiltration is effected in a manner such that a prepared brine 22is introduced as the infiltration material into the drip funnel 16,after which the desiccator 14 is brought to a low pressure of, forexample, 20×10⁻³ bar.

As soon as the desired pressure is reached, the stopcock 22 is opened inthe desired manner. The beaker 12 is filled up to a maximum fill level24 with infiltration material that later penetrates into the blank 10.The penetration is effected principally from the topside and the sidewalls while the underside, which is disposed on the beaker 12, issomewhat less strongly infiltrated.

Although FIG. 1 illustrates a cylindrical blank 10, it is to beunderstood that, in practice, predetermined shaped parts are producedwhich are disposed on the base of the beaker 12 and are wetted withinfiltration material. After an infiltration time of 1 minute, aninfiltration coating in a thickness of 0.3 to 0.6 mm has already beenformed therefrom.

FIG. 2 is a graphical illustration of the infiltration coating depth asa function of the infiltration time. In accordance with the presentinvention, it is advantageous that the coating thickness in many regionscan be accommodated to the requirements. Thus, very fine-sectioned andthin oxide ceramic parts with a decidedly low infiltration coatingthickness which, however, offers a certain translucence but, as well,offers a good securement of the core, can also be worked.

It is advantageous, for example, in connection with an infiltrationdepth of 1 mm or somewhat less, to simulate the natural tooth enamel.The preferred region for the infiltration depth is, however, greaterthan 0.4 mm.

FIG. 3 is a schematic illustration of a sintering oven 26. The sinteringoven comprises a plurality of heating elements 28 and a crucible 30 thatreceives therein the blank 10 after infiltration. Preferably, in aconventional manner, the crucible is provided with a powder coating andthere follows a heating or a finish infiltration of the blank 10 to formthe oxide ceramic part within less than 1 hour, including the heating uptime.

In the hereinafter following descriptions, various embodiments aredescribed in more individual detail.

EXAMPLE 1

A dry press granulate of ZrO₂ powder is used for the raw material forthe blank 10. It is doped with yttrium and comprises other componentssuch as Al₂O₃. The dry press granulates can be, for example, thoseavailable from the TOSOH company with the commercial designation TZ-3YBand TZ-8YB and having a primary crystal size of 280-400 nm and agranulate size of 50 μm but, as well, can be the granulate availableunder the commercial designation of TZ-3Y20AB that is characterized bythe addition thereto of 20% Al₂O₃ and that otherwise corresponds to theother granulates.

In accordance with the following table, powdery oxidized raw materialsin predetermined mole portions are added to the zirconium oxideceramics. Raw Material TZ3YB TZ3YB TZ3YB TZ3YB TZ8YB TZ8YB TZ8YB OxideCeO₂ /mol-% 2.5 5 8 10 15 — — Er₂O₃ 2.5 5 — — — — — CeO₂ + Er₂O₃ /mol-%3 + 3 — — — — — — Sc₂O₃ /mol-% 3 — — — — — — TiO₂ /mol-% 10 15  — — — 1015

In this inventive experiment, cylindrical press forms with innerdiameters of 12 and 16 mm were used. The pressing of the blank 10 waseffected in a conventional manner with pressures of 500, 600 to 1100bar, whereby the press pressure was reached in 5 seconds, then held for15 seconds at the maximum pressure, and then reduced within a further 5seconds.

Thereafter, there followed the pre-solidification step during which, atthe same time, the release was effected and this is shown in thefollowing table, which shows the serially following time segments of thepre-sintering process with the slopes indicated in the left hand column.° C._(Rn)/ ° C._(Rn + 1)/ Heat rate/ Slope ° C. ° C. K min⁻¹ K h⁻¹Time/min Time/h 1 0 320 2.5 150 128 2:08 2 320 470 1 50 150 2:30 3 4701100 2.5 150 252 4:12 4 1100 1100 0 0 20 0:30 560 9:20The powder comprises a binder in the form of a press assistance materialand, via the dry pressing in the following bond release, the introducedbinding material was burnt out and the blank was thus formed with aporous structure. Thereafter, the pre-sintering was performed. After thepre-sintering, a part with 50% thickness depth (TD) was achieved.

The evacuation of the blank 10 was performed in the desiccator 14 with afinish pressure of approximately 20 mbar. Due to the comparatively longevacuation time, which, in any event, amounted to more than 1 hour, thegas enclosed in the porous blank was substantially removed.

Infiltration material based upontetraethoxysilane/tetraethylorthosilicate (TEOS) was used. TEOS was,together with water with a catalyst of aluminum nitratenonhydrate(Al(NO₃)₃)×9 H₂O), mixed with a sol. As a function of themixing time and the subsequent standing time, the sol. reacted slowlyinto a gel and condensed into a glass-similar structure. Ceriumnitratheydrate was also introduced to the actual catalyst.

It was attempted to prepare the infiltration material so that, after theinfiltration into the infiltration coating, a firm gel was quicklyformed which converted after the sintering into a silica glass phase.The infiltration coating was comprised, in accordance with theinvention, principally of tetragonal crystalline zirconium oxide phasesas well as an amorphous glass phases, substantially from condensed TEOS,while the core of the inventive oxide ceramic piece was substantiallycomprised of zirconium oxide with the previously noted doping, whichwas, in any event, predominantly in tetragonal phase.

The attempts with various mixing relationships of TEOS, (Al(NO₃)₃)×9H₂O) as well as Ce(NO₃)₃×9 H₂O revealed the tendency, in connection withlonger mixing times, that the solidification time—that is, the standingtime until solidification—decreased. The sums or totals of the timesamounted to typically 6 to 7 hours, whereby the omission of the ceriumnitratehydrate in certain mixing relationships was able to producesolidification after a mixing time of 3 hours.

The prepared infiltration material was then introduced into the dripfunnel and the stopcock 22 was opened and, in fact, was opened to theextent that the blank was, in any event, fully covered following theintroduction of the sol., but not so far as to permit an excess ofinfiltration material to flow through the drip funnel, as such wouldhave delayed the venting of the desiccator.

The venting followed the complete opening of the stopcock, after whichthe drip funnel 16 became empty.

The infiltration material that had been introduced through thedesiccator and thereafter placed under low pressure initially foamed,whereby the low pressure was maintained.

As can be seen in FIG. 2, the infiltration depth is dependent not onlyupon the viscosity of the introduced infiltration material but, as well,is, in particular, dependent upon the mixing time and the standing alonetime of the infiltration material (the difference between ZIO15 andZIO16b).

It is contemplated that the time for the process is to be selected suchthat the solidification of the infiltration material occurs after orduring the infiltration. It is not critical if the infiltration materialhas already solidified, whereby, as well, in connection with fluidinfiltration material, a thickening of the coating is anticipated inthat, as well, a fluid infiltration material closes the pores of theblank 10.

Infiltration material remainders on the ceramic blank were then removedeasily with a towel and there followed an air-drying step, whereby theinventive examples were subjected to an air-drying of 1 to 2 hours.

The finished sintering followed in the same sintering oven which hadbeen deployed for the pre-sintering and the sintering curve is shown inthe following table in 3 time segments. ° C._(Rn)/ ° C._(Rn + 1)/ Heatrate/ Slope ° C. ° C. K min⁻¹ K h⁻¹ Time/min Time/h 1 0 1000 5 300 2003:20 2 1000 1480 2.5 1450 192 3:12 3 1480 1480 0 0 30 0:30 422 7:02

In this connection, the blank was sealed in a quartz frit—orAl₂O₃—powder bed in an aluminum oxide crucible.

The results showed that the sintered blank comprises an infiltrationcoating thickness which, in dependence upon the infiltration time, is ofvarying thickness.

There was also obtained a good translucence of the oxide ceramic partand, in the interior of the blank, a tetragonal phase with an averagecrystal size of 0.4 to 0.5 micrometers was present.

The smallest achieved infiltration depth, in connection with theabove-noted infiltrate based upon TEOS, amounted to approximately 180micrometers.

EXAMPLE 2

In a modified example, in lieu of TEOS, a zirconium (IV) propylate(Zr(IV)Pr) was deployed. This zirconium (IV) propylate was used in lieuof TEOS and, when subjected to atmospheric pressure with water, wasdriven as zirconium oxide particles out of the pores of the blank. Also,in this connection, the pores could be closed, whereby the crystallineparticles in the pores precipitate out, which corresponds to the actualbase material. The thus achieved minimal coating thickness of theinfiltration coating amounted to approximately 50 micrometers.

EXAMPLE 3

In total, the inventive process produced an oxide ceramic compositeshaped part with high fracture strength, whereby the translucenceproperties corresponded to those of zirconium oxide ceramic (TZP) whichare deployed in connection with the high-temperature isostatic pressprocess. Density Light K_(ic)-Value (in the Transmission (Evans & Ptr/t_(Inf.)/ (core)/ Capability HV 10/ Charles)/ Sample bar min V_(Br)/C gcm⁻³ (comparison) % MPa MPa m^(1/2) A1235 1000 1 1480 6.08 70.7 — —A1237 1000 5 1480 6.10 75.0 — — A1240 1000 2 1480 — — 13220 6.95 A1245 900 1 1480 — — 13055 6.55 A1246  900 1 1480 6.08 72.2 — — Mexoxitunknown unknown unknown 6.07 70.3 12850 6.65 Bio-HIP ZeO₂ (comparisonmeasurement) Denzir unknown unknown unknown 6.10 76.4 12830 6.70 DOHIP-ZrO₂ (comparison measurement) A1253  900 Not 1480 5.88 56.4 — —infiltrated A1254  900 Not 1480 — — 12900 6.17 infiltrated

As can be seen in the foregoing, it is clear that the conventionalsintered examples not produced in accordance with the present inventionexhibit considerably worse properties with respect to light transmissioncapability and fracture strength.

EXAMPLE 4

Additionally, several attempts were made in connection with theinventive process to effect the etching with HF and an etching retentivedesign was produced in correspondence with the length of time. Etchingattempts were undertaken by which the outer coating was completelyetched away and only the inner oxide ceramic core remained. By coveringthe infiltration coating with wax or a polymer coating, it is alsopossible that selected locations can remain unetched.

EXAMPLE 5

In correspondence with the above noted type and manner of shaped parthandling, a cylindrical part with a diameter of 12 mm and a height of 25mm was produced via pressing of a granulate obtained from the Tosohcompany (TZ 3YB) and subsequent pre-sintering at 1100° C. To performthereafter a shaping of the part, a CEREC Inlab milling machineavailable from the Sirona Company was deployed, whereupon thethus-produced shaped part was a crown having excess material. The excessmaterial had to be removed so that, following the shrinking which occursin connection with the sintering and the partial etching away of thecovering coating, an optimal size accommodation or fitment to the modelframe was be produced. In accordance with the present invention, thethus obtained partially sintered and milled part was then provided witha covering coating in a vacuum-configured environment, whereby theapplied material generally penetrated into the outer surface of theporous partially sintered part. During the subsequent sintering processin ambient air at ambient pressure, a finished sintered crown wasproduced that, following partial etching away of the covering coating,exhibited, on the one hand, a retentive design and, on the other hand, agood size accommodation or fitment to the model frame.

FIGS. 4 and 5 each show respective illustrations of the results of theprocess steps in various configurations of the inventive method. Thethus-depicted configurations of the inventive method differ from oneanother with respect to the timing of the machining or trimming step:with respect to the configuration “Technology II” depicted in FIG. 5,the machining or trimming step is performed before the infiltration stepwhile, with respect to the configuration “Technology I” depicted in FIG.4, the trimming step is performed after the finish sintering step. Therespective configuration of the inventive method shown in FIG. 4requires greater tooling efforts in view of the high degree ofsecurement of the substantially completely finished sintered dentalrestoration piece; however, this configuration of the inventive methodoffers a somewhat greater degree of precision.

In all, the demonstrations conducted with respect to the inventivemethod resulted in an oxide ceramic part having a high fracture strengthof 6.95 MPa m^(1/2), whereby the translucence properties werecorrespondingly satisfactory and corresponded to those of oxide ceramicparts that have been produced by high-temperature isostatic pressprocesses.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.While a preferred form of this invention has been described above andshown in the accompanying drawings, it should be understood thatapplicant does not intend to be limited to the particular detailsdescribed above and illustrated in the accompanying drawings, butintends to be limited only to the scope of the invention as defined bythe following claims. In this regard, the term “means for” as used inthe claims is intended to include not only the designs illustrated inthe drawings of this application and the equivalent designs discussed inthe text, but it is also intended to cover other equivalents now knownto those skilled in the art, or those equivalents which may become knownto those skilled in the art in the future.

1. A method for producing an oxide ceramic shaped part, comprising:pressing a selected one of a powder provided with a binding material anda powder mixture of an oxide ceramic into a shaped part; following thepressing of the selected one of the powder and the powder mixture intothe shaped part, pre-sintering the shaped part at substantiallyatmospheric pressure and a temperature of 600 to 1,300° C.; followingthe pre-sintering of the shaped part, evacuating a container and, inparticular, a closed container, in which the pre-sintered shaped part isdisposed with the shaped part having a maximum density of 10 to 90%, andthe container being at an absolute pressure of less than 40 mbar and, inparticular, at between 10 to 30 mbar; and following the evacuation ofthe container, applying an infiltration material onto the shaped partvia infiltration, the infiltration material operating to seal off theshaped part relative to the surrounding atmosphere and the length oftime of the infiltration being, preferably, 1 to 10 minutes.
 2. A methodaccording to claim 1, wherein the organic binding material is anethylene wax, a polyvinyl resin, a polyvinyl pyrrolidone, a polyvinylacetate, a polyvinyl butyral and/or cellulose.
 3. A method according toclaim 1, wherein the further material is formed from a precursor of anon-metallic, inorganic phase or an amorphous glass phase and a solvent,or a connection with a hydrolyzable element of a metal, or an alcoholateof a metal chosen from the group Al, Ti, Zr, and Si, or a precursor of asilicate glass, especially a hydrolyzable silane.
 4. A method accordingto claim 1, wherein, after the infiltration, a further shaping of theshaped part is effected via a material reduction working and/or etching.5. A method according to claim 1, wherein, after the infiltration, theshaped part is finish sintered to a theoretical density of 99.5% at atemperature from 1,300 to 1,550° C.
 6. A method according to claim 1,and further comprising, after a selected one of the infiltration and afinish sintering of the shaped part under environmental pressure,shaping the exterior of the shaped part via at least one of a materialreduction working and etching.
 7. A method according to claim 1, whereinthe outer surface of the shaped part is at least sectionally coated withat least one coating of a mixture material that, in particular, iseffected after the application of a further thermal treatment.
 8. Amethod according to claim 1, wherein an adhesive is applied at leastpartially onto the outer surface of the shaped part and a furthermaterial is secured to the part.
 9. A method according to claim 1, andfurther comprising, following the partial sintering of the part, shapingthe shaped part via a material reduction working with an excess of 10 to50% and, preferably, with an excess of 15 to 30%.
 10. An oxide ceramicpart, comprising a core or a region of a crystalline oxide ceramic phaseand a coating at least partially enclosing the core or a region thereof,which is formed from the crystalline oxide ceramic phase and anon-metallic, inorganic phase (infiltration phase) following thecrystalline oxide ceramic phase.
 11. A shaped part according to claim10, wherein the crystalline oxide ceramic phase is formed substantiallyof oxides or oxide mixtures of the elements zirconium, aluminum, ortitanium, in particular, from a zirconium oxide mixture ceramic ofzirconium oxide and mixtures of metal oxides, the metal oxides of oxidesof the Groups IIIa, IIIb, and IVb of the periodic table of elements, inparticular, from oxides of the metals Hf, Y, Al, Ce, Sc, Er, and/or Ti.12. A shaped part according to claim 10, wherein the crystalline oxideceramic phase is substantially formed of an in particular dopedzirconium oxide ceramic of zirconium oxide with an additive of yttriumoxide, preferably in the range of 0.1 to 10 mole %.
 13. A shaped partaccording to claim 10, wherein the crystalline oxide ceramic phase issubstantially formed of zirconium oxide ceramic with an additive ofyttrium oxide, in the range of 2 to 4 mole %, and, in particular, in therange of 2 to 10 mole % and/or an additive of cerium oxide, preferablyin the range of 2.5 to 15 mole % and/or an additive of erbium oxide,preferably in the range of 2.5 to 5 mole % and/or an additive ofscandium oxide, preferably in the range of 2.5 to 5 mole % and/or anadditive of titanium dioxide, preferably in the range of 0.1 to 15 mole%.
 14. A shaped part according to claim 10, wherein the crystallineoxide ceramic phase is substantially comprised of an aluminum oxide mixceramic formed of aluminum oxide and a mixture of metal oxide and/orpredominately zirconium oxide.
 15. A shaped part according to claim 10,wherein a core or a region of a crystalline oxide ceramic phase with atheoretical density >99.5% and a biaxial strength of not less than 800MPa and a fracture strength of more than 6.5 MPa m^(1/2) is effected.16. A shaped part according to claim 10, wherein at least a portion ofthe core is covered by a coating of an amorphous silicate phase SiO₂, acrystalline silicate phase, or a non-metallic, inorganic phase, wherebythe crystalline silicate phase is comprised of SiO₂ and other metaloxides, especially oxides of the metals of the Groups Ia, Ib, IIa, IIb,IIIa, IIIb, IVa, IVb, and in particular oxides of Al and Ce.
 17. Ashaped part according to claim 10, wherein the coating which at leastpartially encloses the core is a crystalline phase and, especially, ismicro crystalline ZrO₂.
 18. A shaped part according to claim 10, whereinthe thickness of the coating that at least partially encloses the coreis, at a maximum, 90% of the thickness of the finish sintered part,especially 2 to 30% of such thickness.
 19. A shaped part according toclaim 10, wherein the coating is at least partially comprised of thecrystalline oxide ceramic phase and that, especially, the chemicalresistance of this coating to acid is substantially less than that ofthe crystalline oxide ceramic phase in the core.
 20. A shaped partaccording to claim 10, wherein the infiltration phase coating comprisesa greater translucence than the core or the region comprised of thecrystalline oxide ceramic phase.
 21. A shaped part according to claim10, wherein the finish sintered part, in the region of its outersurface, comprises a retentive design formed after an etching step inthe region of the coating that covers the core, whereby the etchingdepth is, in particular, at a maximum equal to the thickness of thecoating covering the core.
 22. A shaped part according to claim 10,wherein the shaped part is configured as a selected one of a dental rootpost in the form of a bracket or abutment, a dental implant, a threesection bridge, a multi-section bridge, a frame for a bridge, analluvial material shaped part, a crown, a partial crown, a partialcomponent of an inlay, a partial component of an onlay, a cap, a reducedcrown, a synthetic joint, an orthopedic implant, and a shaped part of anorthopedic implant.
 23. A shaped part according to claim 10, wherein theshaped part comprises an at least single coated coating formed of amixture material.